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.
Network+ Guide to Networks
7th Edition
Chapter 1
An Introduction to Networking
© 2016 Cengage Learning®. May not be scanned, copied or duplicated, or posted to a
publicly accessible website, in whole or in part.
Objectives
• Identify types of applications and protocols used on
a network
• Distinguish between the client-server and peer-topeer models used to control access to a network
• Describe various networking hardware devices and
the most common physical topologies
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Objectives
• Describe the seven layers of the OSI model
• Explore best practices for safety when working with
networks and computers
• Describe the seven-step troubleshooting model for
solving a networking problem
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How Networks Are Used
• Network services - the resources a network makes
available to its users
– Includes applications and the data provided by these
applications
• Types of applications found on most networks:
– Client-Server
– File and Print Services
– Communications Services
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Client-Server Applications
• Client computer requests data or a service from a
second computer, called the server
• List of several popular client-server applications:
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Web service
Email services
FTP service
Telnet service
Remote Desktop
Remote applications
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Client-Server Applications
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Client-Server Applications
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File and Print Services
• File services - a server’s ability to share data files
and disk storage space
• File server - a computer that provides file services
• Print services - ability to share printers across a
network
– With one printer, less time is spent on maintenance
and management
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Communication Services
• Convergence - using the same network to deliver
multiple types of communications services
• Unified communication (UC) - refers to the
centralized management of multiple network-based
communications
• Three types of communication services:
– Conversational voice - VoIP (Voice over IP)
– Streaming live audio and video
– Streaming stored audio and video
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Communication Services
• Voice and video transmissions are delay-sensitive
– You don’t want to hear or see breaks in transmission
• Voice and video transmission are considered losstolerant
• Network administrators must pay attention to the
quality of service (QoS) a network provides for voice
and video
• Bandwidth - the amount of traffic, or data
transmission activity, on the network
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Controlling Network Access
• Topology - how parts of a whole work together
• Physical topology - mostly applies to hardware and
describes how computers, other devices, and cables
fir together to form the physical network
• Logical topology - has to do with software and
describes how access to the network is controlled
– How users and programs initially gain access to the
network
• Network operating system - controls access to the
entire network
– Required by client-server models
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Peer-to-Peer Model
• Peer-to-peer (P2P) network model - the OS of each
computer on the network is responsible for
controlling access to its resources
– No centralized control
• Computers, called nodes or hosts, form a logical
group of computers and users
– May share resources
– May prevent access to resources
• Each computer user has a Windows local account
– Works only on that one computer
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Peer-to-Peer Model
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Peer-to-Peer Model
• Advantages
– Simple configuration
– Less expensive
• Compared to other network models
• Disadvantages
– Not scalable
– Not necessarily secure
– Not practical for large installations
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Client-Server Network Model
• Resources are managed by the network operating
system (NOS) via a centralized directory database
• Windows domain - a logical group of computers that
a Windows Server can control
• Active Directory (AD) - the centralized directory
database that contains user account information and
security for the entire group of computers
• Global account (a.k.a. global username or network
ID) - a domain-level account assigned by the
network administrator and is kept in AD
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Client-Server Network Model
• A user can sign on to the network from any
computer on the network and gain access to the
resources that AD allows
– This process is managed by Active Directory Domain
Services (AD DS)
• Clients don’t share their resources directly with each
other
– Access is controlled by entries in the centralized
domain database
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Client-Server Network Model
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Client-Server Network Model
• The NOS is responsible for:
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Manages client data, resources
Ensures authorized user access
Controls user file access
Restricts user network access
Dictates computer communication rules
Supplies application to clients
• Server examples
– Windows Server 2012 R2, Ubuntu Server, or Red Hat
Linux
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Client-Server Network Model
• Servers that have a NOS installed require:
– More memory, processing, storage capacity
– Equipped with special hardware
• Provides network management functions
• Advantages relative to peer-to-peer networks
– User credential assigned from one place
– Multiple shared resource access centrally controlled
– Central problem monitoring, diagnostics, correction
capabilities
– More scalable
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Networking Hardware and Physical
Topologies
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LANs and Their Hardware
• Local area network (LAN) - usually contained in a
small space
– Such as an office or building
• Switch - receives incoming data from one of its ports
and redirects it to another port or multiple ports
– Will send the data to its intended destination
• Star topology - all devices connect to one central
device (usually a switch)
• Network interface card (NIC) - a network port used
to attach a device to a network
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LANs and Their Hardware
• A LAN can have several switches
• Backbone - a central conduit that connects the
segments (pieces) of a network
– Might use higher transmission speeds and different
cabling than network cables connected to computers
• Three switches daisy-chained together in a single
line is said to use a bus topology
– However, each switch is connected to computers via
a star topology, making it a star-bus topology
– A topology that combines topologies is known as a
hybrid topology
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LANs and Their Hardware
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LANs and Their Hardware
• Router - a device that manages traffic between two
or more networks
– Can help find the best path for traffic to get from one
network to another
• Routers can be used in small home networks to
connect the home LAN to the Internet
• Industrial-grade routers can have several network
ports, one for each network it connects to
• Difference between router and switch:
– Router is like a gateway between networks
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LANs and Their Hardware
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MANs and WANs
• Metropolitan area network (MAN) - a group of
connected LANs in the same geographical area
– Also known as a campus area network (CAN)
• WAN (wide area network) - a group of LANs that
spread over a wide geographical area
– Internet is the largest and most varied WAN
• MANs and WANs often use different transmission
methods and media than LANs
• PAN (personal area network) - smallest network
– A network of personal devices
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MANs and WANs
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The Seven-Layer OSI Model
• OSI (Open Systems Interconnection) reference
model - a seven-layer model developed to
categorize the layers of communication
• Developed by ISO in the 1980s
• The layers are numbered in order, starting with
Layer 1, the Physical layer at the bottom
– Physical, Data Link, Network, Transport, Session,
Presentation, Application
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The Seven-Layer OSI Model
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Layer 7: Application Layer
• Application layer - describes the interface between
two applications, on separate computers
• Application layer protocols are used by programs
that fall into two categories:
– Provide services to a user, such as a browser and
Web server
– Utility programs that provide services to the system,
such as SNMP that monitor and gather information
about network traffic
• Payload - data that is passed between applications
or utility programs and the OS
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Layer 6: Presentation Layer
• Presentation layer - responsible for reformatting,
compressing, and/or encrypting data in a way that
the receiving application can read
• Example:
– An email message can be encrypted at the
Presentation layer by the email client or by the OS
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Layer 5: Session Layer
• Session layer - describes how data between
applications is synched and recovered if messages
don’t arrive intact at the receiving application
• The Application, Presentation, and Session layers
are intertwined
– Often difficult to distinguish between them
• Most tasks are performed by the OS when an
application makes an API call to the OS
– Application programming interface (API) call is the
method an application uses when it makes a request
of the OS
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Layer 4: Transport Layer
• Transport layer - responsible for transporting
Application layer payloads from one application to
another
• Two main Transport layer protocols are:
– TCP (Transmission Control Protocol) - makes a
connection with the end host, checks whether data
was received; called a connection-oriented protocol
– UDP (User Datagram Protocol) - does not guarantee
delivery by first connecting and checking whether
data is received; called a connectionless protocol
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Layer 4: Transport Layer
• Protocols add their own control information in an
area at the beginning of the payload (called a
header)
• Encapsulation - process of adding a header to the
data inherited from the layer above
• The Transport layer header addresses the receiving
application by a number called a port number
• If message is too large, TCP divides it into smaller
messages called segments
– In UDP, the message is called a datagram
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Layer 3: Network Layer
• Network layer - responsible for moving messages
from one node to another until reaches destination
• IP adds its own Network layer header to the
segment or datagram
– The entire Network layer message is called a packet
• IP address - assigned to each node on a network
– Network layer uses it to uniquely identify each host
• IP relies on several routing protocols to find the best
route for a packet to take to reach destination
– ICMP and ARP are examples
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Layer 2: Data Link Layer
• Layers 2 and 1 are responsible for interfacing with
physical hardware on the local network
– Protocols at these layers are programmed into
firmware of a computer’s NIC and other hardware
• Type of networking hardware or technology used on
a network determine the Link Layer protocol used
– Ethernet and Wi-Fi are examples
• The Link layer puts control information in a Link
layer header and at the end of the packet in a trailer
– Entire Link layer is called a frame
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Layer 2: Data Link Layer
• MAC (Media Access Control) address - hardware
address of the source and destination NICs
– Also called a physical address, hardware address, or
Data Link layer address
– Embedded on every network adapter and are
considered short-range addresses that can only find
nodes on the local network
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Layer 1: Physical Layer
• Physical layer - simplest layer and is responsible for
sending bits via a wired or wireless transmission
• Can be transmitted as:
– Wavelengths in the air
– Voltage on a copper wire
– Light (via fiber-optic cabling)
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Protocol Data Unit or PDU
• Protocol data unit (PDU) - the technical name for a
group of bits as it moves from one layer to the next
and from one LAN to the next
– Technicians loosely call this group of bits a message
or a transmission
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Summary of How the Layers Work
Together
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Summary of How the Layers Work
Together
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Staying Safe When Working with
Networks and Computers
• Network and computer technicians need to know
how to protect themselves
– As wells as protect sensitive electronic components
• This section takes a look at some best practices for
safety
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Emergency Procedures
• Know the best escape route or emergency exit
• Fire Suppression Systems - have a fire suppression
system in the data center that includes:
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Emergency alert system
Portable fire extinguishers
Emergency power-off switch
Suppression agent
• Fail Open or Fail Close - does the security system
allow access during a failure (fail open) or deny
access during the failure (fail close)
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Emergency Procedures
• Material Safety Data Sheet (MSDS) - explains how
to properly handle substances such as chemical
solvents and how to dispose of them
– Includes information such as physical data, toxicity,
health effects, first aid, storage, shipping, disposal,
and spill procedures
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HVAC Systems
• Heating, ventilation, and air conditioning (HVAC)
system - controls the environment in a data center
– Including the temperature, humidity, airflow, and air
filtering
• HVAC system must provide acceptable temperature
and humidity ranges for devices that might overheat
or fail due to high humidity
• HVAC systems and network cabling often occupy
the space above the ceiling or below the floor in a
data center
– Called the plenum
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Protecting Against Static Electricity
• Computer components are grounded inside a
computer case
• Sensitive electronic components can be damaged
by electrostatic discharge (ESD)
• Static electricity can cause two types of damage:
– Catastrophic failure - destroyed beyond use
– Upset failure - shorten the life of a component
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Protecting Against Static Electricity
• Before touching a component, ground yourself by:
– Wearing an ESD strap around your wrist that clips
onto the chassis or computer case
– Touching the case before touching any component
inside the case
– Storing a component inside an antistatic bag
• In addition to protecting against ESD, always shut
down and unplug a computer before working inside
it
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Installation Safety
• Lifting Heavy Objects - follow these guidelines:
– Decide which side of object to face so load is most
balanced
– Stand close to the object with your feet apart
– Keep your back straight, bend knees and grip load
– Lift with your legs, arms, and shoulders (not your
back or stomach)
– Keep the load close to your body and avoid twisting
your body while you’re holding it
– To put the object down, keep your back as straight as
possible and lower object by bending your knees
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Installation Safety
• Rack Installations - switches, routers, servers, and
patch panels can be installed in racks
– Follow device manufacturer’s guidelines for
requirements for the rack and the direction for
installation
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Installation Safety
• General directions for safely installing rackmountable devices:
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Engage brakes on rack wheels, if applicable
Wear an ESD strap
Place the device in the rack for good airflow
Device must be well grounded
Pay attention to tools as you work so they don’t
accidentally fall into a rack of expensive equipment
– Install fan trays so that air flows in the same direction
as the fans inside the device
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Installation Safety
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Electrical and Tool Safety in Data
Centers
• Electrical and tool safety is generally regulated by
OSHA (Occupational Safety and Health
Administration)
• OSHA guidelines when using power tools:
– Wear personal protective equipment (PPE)
– Keep all tools in good condition and properly store
tools not in use
– Use the right tool for the job and operate the tool
according to the manufacturer’s instructions
– Watch out for trip hazards, so you and others don’t
stumble on a tool or cord
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Troubleshooting Network Problems
• Troubleshooting steps used by most expert
networking troubleshooters:
– Identify problem
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Gather information
Identify symptoms
Question users
Determine if anything has changed
– Establish theory of probable cause
• Question the obvious
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Troubleshooting Network Problems
• Troubleshooting steps (cont’d)
– Test theory to determine cause
• If theory confirmed, determine next steps
• If theory not confirmed, establish new theory or
escalate
– Establish action plan
– Implement solution or escalate the problem
– Verify full functionality
• Implement preventative measures if applicable
– Document findings, actions, outcomes
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Summary
• Networks provide a wide range of services, including
client-server applications, file and print services, and
communications services
• File and print services enable multiple users to
share data, storage areas, and printers
• Traditional peer-to-peer networks are usually simple
and inexpensive to set up
• The client-server model for access control relies on
a centrally administered server using a NOS that
manages shared resources for multiple clients
– More complex and expensive to install
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Summary
• A LAN is a network of computers and other devices
that can directly address all other nodes
• In a star topology, all computers and network
devices connect to one central device
• A backbone is a central conduit that connects parts
of a network and might use the bus topology
• A router manages traffic between two or more LANS
• LANS can be interconnected to form WANS, which
traverse longer distances in two or more
geographical areas
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Summary
• The seven layers of the OSI model are Application,
Presentation, Session, Transport, Network, Data
Link, and Physical
• At Layers 7,6, and 5, data and its control information
is known as the payload
• A message at the Transport layer is called a
segment in TCP and a datagram in UDP
• An IP transmission is called a packet
• A message at the Data Link layer is called a frame
• Some switches operate at the Data Link layer and
routers operate at the Network layer
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Summary
• A fire suppression system can include an
emergency alert system, portable fire extinguishers,
an emergency power-off switch, and suppression
agents
• HVAC systems are responsible for controlling
humidity and temperature in a data center
• When working with sensitive components, protect
against ESD by using an ESD strap
• Troubleshooting problems and their solutions are
documented in a call tracking system
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